1. Field of the Invention
This invention relates to the production of crimped filaments made from long chain molecule thermoplastics materials and relates particularly, but not exclusively to fibres made from polypropylene.
2. Description of Related Art
Filaments made from long chain molecule thermoplastics materials are well known in the art and are generally extruded through holes in a spinneret plate from a body of the molten plastics material above the spinneret plate. When produced in this manner, the filaments are essentially straight and without crimp. Whilst continuous straight filaments, without crimp, can be used for a number of commercial processes, a crimping of the filament is highly desirable for a number of commercial applications, in particular in the clothing or woven material industries.
One known method for applying a crimp to a continuous filament is to pass the filament, in heated conditions, between a pair of meshing gear wheels but the crimp obtained by the gear wheels is very limited and lies in only one plane of the filament. If the filament is rotated about its axis whilst passing through the gear wheels a helical crimp can be produced but said crimp will require the additional expense of providing a means of rotating each filament and the crimp is relatively weak.
In another known method for crimping filaments the filaments, whilst in heated condition, are cooled on one side and, as the filaments cool, differential stresses will be induced across the diameter of the filaments. When the drawing tension is released from such filaments a wavy, or helical, crimp will develop but, in practise, the degree of crimp applied to and retained by such filaments is relatively small.